Vifa datasheets don't agree with WinISD...

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I was reading through the datasheet for my Vifa P17WJ-00-08's that I'm going to use, but I noticed that the graphs it shows for frequency responce don't agree with the graphs WinISD show me for an identical box design and tuning frequency. I checked the values in the WinISD program and the only thing that isn't exactly as listed in the datasheet is Le, and it's only off by 0.05mH, so I really don't understand why this is. Is WinISD just not as accurate as the guys at Vifa (my guess)? Or is the Vifa datasheet at fault (I doubt it, but I feel I should make sure I don't make any mistakes)?
diyAudio Moderator Emeritus
Joined 2001
I went to Vifa site and the only graph they had was for unenclosed response.

I simulated unenclosed response on WinISD by calling for a closed box of 20 cubic feet. That is so large that for this woofer, it is the same as unenclosed.

It seems to be an 88 dB @ 1W/1M speaker. Both of the plots seem to agree with each other at beginning of rolloff, and at 50 Hz, 30 Hz and 20 Hz.

With no simulations for a specific box, this was the best I could do.

I will put Vifa's free air response chart and WinISD's equivalent here and see what you think.

Don't forget on Vifa's real-life version, there are some peaks in the response so you have to sort of average those out when you compare them to the WinISD chart. When you do that, there seems to be reasonably good agreement between the two charts.

Here is Vifa's chart.


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I was checking the graph on the second page of under the applications part, bass reflex synthesis. If you take a look at it, I was looking at 30l with 45Hz tuning (5cmx4xm port).

The WinISD one (seen below) with the same box specs shows a 1dB peak for a while before the rolloff (I know if just 1dB, but I'm curious why the two graphs aren't identical) while vifas graph doesn't show any peaks at all.

As for telling you how it goes planet10, I will do, but it might be a while since I got rid of my entire system and a new one is in the making (it's a simultaneous project kinda thing, the speakers, amp, xover, preamp, etc). Although it is coming along rather quickly, I've gotten all parts (some are in the mail, should arrive shortly) except my heatsinks which are still being made. Roughly 100lbs of metal to cool down my class-a's :)...


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diyAudio Moderator Emeritus
Joined 2001
If anything, I am surprised the hump isn't bigger.

The Vifa has a Qts of .4.

Ideal for a Vb equal to Vas.

Here, Vb is 60% of Vas.

When a speaker goes into a box smaller than it's ideal match, you generally get a hump in the response.

If anything, Parts Express would seem to be off.
diyAudio Moderator Emeritus
Joined 2001
Please ignore above post.

Don't know what I was looking at-the Thiele-Small parameters are the same as you said, Joe Bob.

Here is another anomaly. According t WinISD, a 5cm dia tube of 4 cm length tunes a 30 liter enclosure to 50 Hz. This gives a much bigger hump.

However, the response will be 6 dB down at 40 Hz, which agrees with the graph at Parts Express.

Here is the WinISD simulation with the port made to be 5 cm diameter times 4 cm long.

Go figure!


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diyAudio Moderator Emeritus
Joined 2001
The Java based "Port Designer" at Steve Ekblad's site says that a 5 cm dia vent of 4 cm length tunes a 30 liter box to 51 Hz-close enough to WinISD's 50 Hz.

The Port Designer uses cubic feet and inches.

30 liter = 1.06 cu ft.
5 cm = 2 in
4 cm = 1.6 in

I'll bet most programs agree with WinISD. I think Vifa made a mistake, or did the chart when the Thiele-Small parameters were different from now and never changed the chart.
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